排序方式: 共有33条查询结果,搜索用时 70 毫秒
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Barkan A Tittel FK Mittleman DM Dengler R Siegel PH Scalari G Ajili L Faist J Beere HE Linfield EH Davies AG Ritchie DA 《Optics letters》2004,29(6):575-577
We have measured the spectral linewidths of three continuous-wave quantum cascade lasers operating at terahertz frequencies by heterodyning the free-running quantum cascade laser with two far-infrared gas lasers. Beat notes are detected with a GaAs diode mixer and a microwave spectrum analyzer, permitting very precise frequency measurements and giving instantaneous linewidths of less than -30 kHz. Characteristics are also reported for frequency tuning as the injection current is varied. 相似文献
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We describe observations of the amplitude and phase of an electric field diffusing through a three-dimensional random medium, using terahertz time-domain spectroscopy. These measurements are spatially resolved with a resolution smaller than the speckle spot size and temporally resolved with a resolution better than one optical cycle. By computing correlation functions between fields measured at different positions and with different temporal delays, it is possible to obtain information about individual scattering events experienced by the diffusing field. This represents a new method for characterizing a multiply scattered wave. 相似文献
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Propagation of single-cycle terahertz pulses in random media 总被引:1,自引:0,他引:1
We describe what are to our knowledge the first measurements of the propagation of coherent, single-cycle pulses of terahertz radiation in a scattering medium. By measuring the transmission as a function of the length L of the medium, we extract the scattering mean free path l(s)(omega) over a broad bandwidth. We observe variations in l(s) ranging over nearly 2 orders of magnitude and covering the entire thin sample regime from L/l(s)<1 to L/l(s)~10 . We also observe scattering-induced dispersive effects, which can be attributed to the additional path traveled by photons scattered at small angles. 相似文献
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We report the experimental and theoretical study of the dispersive behavior of surface plasmon polaritons (SPPs) on cylindrical metal surfaces in the terahertz frequency range. Time-domain measurements of terahertz SPPs propagating on metal wires reveal a unique structure that is inconsistent with a simple extrapolation of the high frequency portion of the dispersion diagram for SPPs on a planar metal surface, and also distinct from that of SPPs on metal nanowires observed at visible and near-infrared frequencies. The results are consistent with a numerical solution of Maxwell's equations, showing that the dispersive behavior of SPPs on a cylindrical metal surface at terahertz frequencies is quite different from that of SPPs on a flat surface. These findings indicate the increasing importance of skin effects for SPPs in the terahertz range, as well as the enhancement of such effects on curved surfaces. 相似文献
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In many generic combustion models, one finds that a combustionwave will develop with a specific wave speed. However, thereare possible initial temperature profiles which do not evolveinto such waves, but rather die out to the ambient temperature.There can exist, in some models, a clear distinction betweenthose initial conditions that do evolve into combustion wavesand those that do not; this is sometimes referred to as thewatershed initial condition. When fuel consumption is consideredto be negligible, analytical methods can be used to obtain theexact watershed. In this paper, we consider the problem of determiningpseudo-watersheds and ascertaining the relationship betweenthese pseudo-watersheds and the exact watersheds. In the processa novel weight-function approach for infinite spatial domainsis developed. 相似文献
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Recent advances in terahertz imaging 总被引:10,自引:0,他引:10
D.M. Mittleman M. Gupta R. Neelamani R.G. Baraniuk J.V. Rudd M. Koch 《Applied physics. B, Lasers and optics》1999,68(6):1085-1094
We review recent progress in the field of terahertz “T-ray” imaging. This relatively new imaging technique, based on terahertz
time-domain spectroscopy, has the potential to be the first portable far-infrared imaging spectrometer. We give several examples
which illustrate the possible applications of this technology, using both the amplitude and phase information contained in
the THz waveforms. We describe the latest results in tomographic imaging, in which waveforms reflected from an object can
be used to form a three-dimensional representation. Advanced signal processing tools are exploited for the purposes of extracting
tomographic results, including spectroscopic information about each reflecting layer of a sample. We also describe the application
of optical near-field techniques to the THz imaging system. Substantial improvements in the spatial resolution are demonstrated.
Received: 29 January 1999 / Published online: 7 April 1999 相似文献
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R. Piesiewicz C. Jansen S. Wietzke D. Mittleman M. Koch T. Kürner 《International Journal of Infrared and Millimeter Waves》2007,28(5):363-371
We present measurements of the frequency dependent refractive index and absorption coefficient of a variety of common building
and plastic materials between 100 and 1000 GHz. Accurate knowledge of the material parameters is indispensable for the modeling
of bound media propagation phenomena including single and multiple reflections, transmission, diffraction and scattering effects.
These models are for example required for a reliable channel simulation to investigate signal propagation in future wireless
communication systems operating with Gigabit data rates at frequencies above 100 GHz. Also, the measured material parameters
can be used for the investigation and development of THz system components. 相似文献
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We describe broadband coherent transmission studies of two-dimensional photonic crystals consisting of a hexagonal array of air holes in a dielectric slab in a planar waveguide. By filling several of the air holes in the photonic crystal slab, we observe the signature of a defect mode within the stop band, in both the amplitude and phase spectra. The experimental results are in reasonable agreement with theoretical calculations using the transfer matrix method. 相似文献